Conveniently, your integration limits are $(0,4)$ so the inside absolute value can be ignored. You are left with the following:
$$\int_0^4 |x^2 - 2x| \ dx = \int_0^4x\cdot|x-2|\ dx$$
$$= \int_0^2 x\cdot(2-x)\ dx + \int_2^4x\cdot(x-2) \ dx$$
I leave the rest to you.
Conveniently, your integration limits are $(0,4)$ so the inside absolute value can be ignored. You are left with the following: $$\int_0^4 |x^2 - 2x| \ dx = \int_0^4x\cdot|x-2|\ dx$$ $$= \int_0^2 x\cdot(2-x)\ dx + \int_2^4x\cdot(x-2) \ dx$$ I leave the rest to you.